Signal Level Needed For Soarview

bob1163

Does anybody know the min levels required to give a stable Saorview picture, I friend had 50dB at the decoder but the picture was breaking up from time to time. I managed to increase it to 54dB and it seems to be ok but I was wandering if there was a recommended signal level and does the transmitter make any difference. I was looking online but cant find any information on this. Thanks

lucernarian

61 dBuV is what RTÉ specify as a field signal strength needed for reliable reception at 10 metres agl on a modest-gain aerial. Based on the coverage maps they use anyway.

Vince Cable

bob1163 wrote: »

Does anybody know the min levels required to give a stable Saorview picture

45 dBuV minimum at the receiver afaik, section 1.4 here

You probably have interference issues/poor SNR (Signal to Noise Ratio) or the figures you are getting aren't accurate.
Could also be caused by poor installation, bad connections etc.

The Cush

Similar posted here recently -
http://www.boards.ie/vbulletin/showthread.php?p=72100713#post72100713

lucernarian

The Cush wrote: »

Similar posted here recently -
http://www.boards.ie/vbulletin/showthread.php?p=72100713#post72100713

I would have thought the minimum signal at the receiver level would have to depend on the type of modulation used and therefore the SNR needed, assuming that background/thermal noise at the receiver level is constant.

Vince Cable

Wouldn't plain signal level have more to do with receiver design than modulation?

Obviously it's more complicated than 'I have minimum signal level therefore I'm guaranteed perfect reception'.
I would think most installers would aim for the mid 50s dB as a minimum, in practice.

AstralTV

min sig level at receiver input 45db recommended 50db

C/N for reliable reception >26db

BER 2E-4 (2 ERRORS / 10000 BITS)

bob1163

Thanks for all your help. by the way does the transmitter make a difference as i can get signal from two, one very powerful but far away and one not so powerful but closer. If both have the same signal level does it make a difference which one I pick

Vince Cable

The closer transmitter might be less affected by varying propagation conditions caused by weather.
Which 'powerful' tx are you referring to? If it's Mount Leinster & you're near the coast, it's probably best avoided due to interference from Wales.

Souriau

AstralTV wrote: »

min sig level at receiver input 45db recommended 50db

C/N for reliable reception >26db

BER 2E-4 (2 ERRORS / 10000 BITS)

Is db and dbµv the same or different?
As the Digiair db give readout of dbµv

AstralTV

this may help,

http://www.aerialsandtv.com/decibels.html

winston_1

Souriau wrote: »

Is db and dbµv the same or different?
As the Digiair db give readout of dbµv

db on it's own is meaningless. db is a ratio so to have any meaning you have to quote a reference. dbuv is a ratio of the quoted figure with respect to 1uv.

Noise levels are often quoted in db with no reference which is also meaningless though it is often assumed to be with reference to the threshold of human hearing.

watty

When we talk RF, the NF (Noise Figure) is the dB of excess noise compared to an theoretically perfect receiver.

Both at same temperature, bandwidth and in perfect faraday cage with perfect input matching at same temperature.

i.e. the NF is noise generated in the real electronics.

It's got nothing to do with threshold of hearing.

Noise Levels of sound are not noise levels, but Sound pressure levels. It need not be "noise" in sense of random. It's the power level above a reference of 20 µPa RMS, regarded as threshold of hearing.
90dB is heavy traffic, 0.001 W
130dB is threshold of pain, about 10W
A live trumpet (jazz horn) is about 3W.
Good "speakers" are only about 1% efficient, so 3W of live horn needs a 300W amplifier / Speaker! Bose are the least efficient and need much more power. Efficiency says nothing about reproduction quality.

With Digital and Analogue TV it can be more useful to know the Signal to Noise (Eb/No or quality or bit error rate).

You also need to know the absolute level too as if it's too low, then you can't split the signal or drive any coax at all without amplification with a low noise amplifier. If it's too high it may need attenuated or receivers or amplifiers may overload.

dBmW in 50 Ohms, 75 Ohms, or 300 Ohms is one reference.

Field strength is usually reference to 1uV/m (microvolts per meter).
60dBu is thus 1mV per meter.

Coverage plot contours are usually dBu (reference microvolt per meter).

On practical systems dBm (reference 1mW in 50, 75, 300, 600 Ohms, whatever the cable & equipment impedance is).

A dBu reading only makes sense on a calibrated aerial with exact known gain.

for example if the minimum spec is 35dBu for Digital and the signal strength is 20dBu, then an aerial with a gain of 15dB is needed. An amplifier of 15dB will not work as that amplifies the noise and interference too.

If the cable loss is 18dB from aerial to equipment, then can't put much more than 18dB of mast head gain. If the signal is 20dB more than needed, then no preamp is needed.

So it's more useful to know the dBm needed and the minimum SNR for analogue and minimum Eb/No (digital SNR) or maximum Bit Error Rate.

Different transponders or multiplex from same source with same power may need different SNR as the FEC and APSK/QPSK or QAM/PSK modulation levels may be different.

AstralTV

winston_1 wrote: »

db on it's own is meaningless. db is a ratio so to have any meaning you have to quote a reference. dbuv is a ratio of the quoted figure with respect to 1uv.

Noise levels are often quoted in db with no reference which is also meaningless though it is often assumed to be with reference to the threshold of human hearing.

After 20 odd years of using db in my daily work it is far from meaningless to me & all the people I have worked with, plus this Is the terrestrial forum, :rolleyes: